The subject invention is directed to apparatus for filtering of undesirable components such as hot gases, charged particles and ultraviolet radiation, from the output of a pulsed plasma x-ray source.
In applications such as x-ray lithography, x-ray microscopy and materials evaluation, there is a need to eliminate undesirable components from the output of an x-ray source. By way of background with respect to lithography, presently integrated circuits are manufactured using ultraviolet light lithographic systems. In such systems, the circuit pattern is determined, and a mask is prepared in accordance with the pattern. The mask is a thin plate having transparent and opaque sections according to the pattern. Upon illumination of the mask with the ultraviolet light, an image is projected onto a silicon wafer having a photoresist coating. A relief pattern replicating the mask is provided upon chemical treatment to remove either the exposed or unexposed resist (depending upon the type of resist process employed). Subsequent etching, doping or metallization steps impart the desired electrical characteristics to the wafer, and the remaining resist is removed, resulting in the formation of one level of an integrated circuit.
Commercially available ultraviolet light lithography systems offer pattern resolution on the order of 1.5-2 microns. Such a level of resolution is adequate for the production of integrated circuits such as a 64K random-access memory; however, for still larger scale integrated circuitry, lithographic systems providing submicron pattern resolution are needed, if the products are to be kept small. An x-ray lithography system incorporating a pulsed plasma source provides the finer resolution desired. The system converts an electrical input to x-rays using the phenomenon of gas jet z-pinch. In this method of x-ray generation, a burst of a gas (such as nitrogen, krypton or argon) is expanded using a nozzle, in concert with the fast discharge of a capacitor bank through the expanding gas. A high current discharge generates an intense magnetic field which radially compresses the plasma. The result is a dense, high temperature plasma which is a very intense source of desirable x-rays with comparatively long wave lengths and hence low penetrating power (commonly known as soft x-rays). Unfortunately, generated along with the x-rays are hot gases, charged particles and utlraviolet light. These components must be removed to avoid overheating and degradation of components of the system and loss of the desired degree of pattern resolution.
One proposed x-ray lithography system employs arrays of vertical and horizontal grazing incidence mirrors between the r-ray source and the mask to substantially collimate soft x-rays from the source. This system incorporates filters for adjusting the intensity and spectrum of the output beam. For further information regarding the structure and operation of such an x-ray lithography system, reference may be made to U.S. Pat. No. 4,242,588.